void main() {
  Person p = new Person('李四', 21, '女', '上海');
  p.say();
}

class Person {
  String? name;
  int? age;
  String? gender;
  String? address;

  // Person(String? name ,int?age,String?gender,String?address) {
  //   this.address=address;
  //   this.age=age;
  //   this.gender=gender;
  //   this.name=name;
  // }
  Person(this.name, this.age, this.gender, this.address);
  say() {
    print('我叫$name,我今年$age岁,我是一个$gender,我住在$address');
  }
}
